Heating Control System for A Screed

ABSTRACT

A control system for heating a screed assembly of a paving machine is provided. The control system includes a plurality of resistive heating elements positioned adjacent to a screed plate of the screed assembly. An electrical power supply is selectively connected with the resistive heating elements via switches operated by a controller. The controller is responsive to inputs from at least manual switches and temperature sensors. The controller is configured to automatically adjust the temperature of the screed plate by selectively energizing fewer than all of the resistive heating elements at a time.

TECHNICAL FIELD

The invention relates to paving machines and, more particularly to aheating control system for a screed of a paving machine.

BACKGROUND

Paving machines are generally used for laying a heated paving material,such as bituminous aggregate mixtures or asphalt, onto a roadbed andspreading the heated paving material to achieve a road with a uniform,smooth surface. After the heated asphalt is laid it is compacted andcools so that the road becomes passable by vehicles.

The paving machines include a screed assembly for spreading the heatedmaterial. The screed assembly has one or more screed plates, and thesescreed plates are at times heated for ease in manipulating the heatedpaving material. The temperature of the screed plates is important,because if the temperature is too high, the screed may warp or theheated paving material may be damaged. Also, if the temperature is toolow, the heated paving material adheres to the screed and is difficultto spread and compact. Generally, the screed plates should be heated toa temperature close to the temperature of the heated asphalt material.

Controllers have been developed for controlling the temperature of thescreed plates. Published patent application WO 00/47822 is directed to aheating control system that automatically regulates the screed platetemperature by adjusting current flow through resistive heating elementsfor each of the screed plates. However, when the temperature of a screedplate drops below a predetermined value, the entire screed plate isheated even though only a section of the screed plate may requireheating. In addition, several screed plates may be heatedsimultaneously. Heating the entire screed plate or several screed platessimultaneously drains the power supply, which is used for otherfunctions, such as lighting, of the paving machine, and such generalheating is inefficient.

The present invention is directed to overcome one or more of theproblems as set forth above.

SUMMARY OF THE INVENTION

A heating control system for heating a screed assembly of a pavingmachine is provided. The screed assembly includes a screed plate. Theheating control system includes a plurality of resistive heatingelements attached to the screed assembly and positioned adjacent to thescreed plate. An electrical power supply is connected to the pluralityof resistive heating elements. A controller is connected to theplurality of resistive heating elements to automatically adjust thetemperature of the screed plate by selectively energizing one or more ofthe plurality of resistive heating elements.

A method for heating the screed assembly includes sequentially andautomatically energizing one or more of the plurality of resistiveheating elements at a time to achieve a predetermined screed platetemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a screed assembly, embodying the present invention,that is towed by an asphalt paving machine;

FIG. 2 is a schematic view of a screed heating control system of thepresent invention; and

FIG. 3 is a flow diagram illustrating a method of operation of theheating control system of the present invention.

DETAILED DESCRIPTION

A screed assembly 10 for a paving machine 12, only a portion of whichis, is shown in FIG. 1. The paving machine 12 includes a heating controlsystem 14 as shown in FIG. 2. The screed assembly 10 includes a mainscreed 16 and left and right screed extensions 18,20. It should beunderstood that left and right screed extensions 18,20 are shown asbeing front mounted but can be either front or rear mounted extensions.In an extended mode the left and right screed extensions 18,20 extendoutwardly from either side of the main screed 16.

The main screed 16 is made up of first and second sections 30,32 one oneach side of a longitudinal central axis 34. The left and right screedextensions 18,20 are slidably mounted to first and second sections 30,32of the main screed 16 respectively and include first and second screedplates 36, 38. The left and right screed extensions 18,20 also includeleft and right screed plates 40,42.

The screed assembly 10 functions to spread paving material distributedby the paving machine 12 onto a roadbed. In order to achieve optimumworkability of the paving material, the temperature of the screed plates36,38, 40,42 should be maintained within a predetermined temperaturerange. This predetermined temperature range is for exemplary purposes,between 250-310° F., however, other temperature ranges may be set. Theheating control system 14 automatically controls the temperature ofscreed plates 36,38, 40,42 and is illustrated in detail in FIG. 2.

The heating control system 14 includes resistive heating elements 50a-50 d, 52 a-52 d, 54 a-54 d, 56 a-56 d, an electrical power supply 60and a controller 62. Power supply 60 is any suitable AC or DC powersource that is connected, as by wire, to the controller 62. The powersupply 60 shown in FIG. 2, utilizes a 24V DC power supply, but othervoltages and power sources may be used, as would be known in the art.The controller 62 may include a typical microprocessor and memory, andcan be programmed or hard-wired to provide the functions discussedbelow.

As illustrated in FIG. 2, the four resistive heating elements 50 a-50 d,52 a-52 d are disposed on first and second screed plates 36,38respectively, and four resistive heating elements 54 a-54 d, 56 a-56 dare disposed on the left and right screed plates 40,42 respectively.However, the present invention is not limited to this construction andother numbers of resistive heating elements may be provided for eachscreed plate.

The resistive heating elements 50,52,54,56 with subscript a & b aredisposed on forward portions of the screed plates 36,38,40,42 and theresistive heating elements 50,52,54,56 with subscript c & d are disposedon rearward portions of the screed plates 36,38,40,42. As used hereinthroughout, forward refers to the side of the screed plate that isclosest in proximity to the paving machine 12, while rearward refers tothe farthest away from the paving machine 12. In use, the screedassembly 10 is pulled in the forward direction as indicated by arrow 58in FIG. 1.

The heating control system 14 also includes inputs to and outputs fromthe controller 62. An on/off switch 70, a both/rear-only switch 72 and awarm-up switch 74 provide one set of inputs. Each of the switches 70,72and 74 selectively connect the electrical power supply 60 to respectiveinput connectors of the controller 62. Temperature switches 80,82,84,86,which are normally open, provide another set of inputs. The function andoperation of each of these switches is provided in further detail below.

The temperature switches 80,82,84,86 are provided, one for the first andsecond screed plates 36,38 of the main screed 16, and one for the leftand right screed plate 40,42 of the left and right screed extensions18,20. A temperature sensor 90,92,94,96 is provided with eachtemperature switch 80,82,84,86 to detect the temperature of thecorresponding screed plate 36,38,40,42. Temperature switches 80,82,84,86will close when the detected temperature falls below a firstpredetermined temperature Ta, e.g., Ta=250° F., and will open when thetemperature reaches a second predetermined temperature Tb, e.g., Tb=310°F.

As shown in FIG. 2, eight outputs (1-8) from the controller 62 areprovided respectively to eight solenoid relay switches, i.e., fourforward output switches 100, 102,104,106 and four rearward outputswitches 110,112,114,116. Two output switches (100,110; 102,112) areassigned for each respective section 30,32 of the main screed plate 16.Similarly, two output switches (104,114; 106,116) are providedrespectively for the left and right screed extensions 18,20. The outputswitches are normally open, and the output switches are closed inresponse to signals provided from the controller 62. When closed, theswitches connect an AC power generator 118 to the respective resistiveheating elements 50 a-50 d, 52 a-52 d, 54 a-54 d, 56 a-56 d, thusselectively heating the screed plates 36,38,40,42 in response to thetemperature being below a threshold temperature Ta. Similarly, when thetemperature then increases above the second threshold temperature Tb,the closed switch opens and AC power is disconnected from the heatingelement.

Each temperature switch 80,82,84,86 controls two corresponding outputswitches of the associated screed plate. As shown in FIG. 2, temperatureswitch 80 corresponds to the forward and rearward output switches100,110 of the first screed plate 36, the forward output switch 100corresponds to the forward resistive heating elements 50 a, 50 b and therearward output switch 110 corresponds to the rearward resistive heatingelements 50 c, 50 d. Thus, the heating of the forward and rearwardresistive heating elements on the first screed section 30 is separatelycontrolled by the two respective output switches 100, 110. Similarly,temperature switches 82,84,86 correspond to the second screed section 32and the left and right screed extensions 18,20 respectively.

FIG. 3 is a flow chart illustrating a control diagram for the presentinvention. First, the paving machine is turned on (S1), and either theauto mode or the warm-up mode is turned on (S2). If the warm-up mode isturned on, it is determined whether the rear-only mode is turned on(S3). If yes, all of the rearward heating elements are energizedsimultaneously (S4) until the screed plates reach a predeterminedtemperature Tb, e.g., 310° F. If no, all of the heating elements areenergized simultaneously (S5) until the screed plates reach apredetermined temperature Tb, e.g., 310° F. After all of the desiredheating elements have been heated so that the screed plates reach apredetermined temperature Tb, the controller is automatically set to theauto mode.

In the auto-mode, it is determined whether the rear-only mode is turnedon (S7). If yes, only the rearward heating elements are to be heated.Each rearward heating element is heated in sequence so that the screedplates are heated in sequence. Of course, if only one screed plate ispresent, this step may refer to only one rearward heating element beingheated at a time, whereas if multiple screed plates are present, thoserearward heating elements associated with one screed plate are heatedtogether, followed by the rearward heating elements of a second screedplate, etc.

Next, the temperatures of the screed plates are monitored (S9) and if itis determined that the temperature has fallen below a predeterminedtemperature Ta, e.g., 250° F., the rearward heating elements of thatscreed plate are energized (S11). If the temperature is within anacceptable range, the monitoring of the screed plate temperature iscontinued (S9) until it requires heating.

A similar method is followed if the rear-only mode is not on in the automode. Specifically, all of the heating elements for all of the screedplates are heated in sequence (S12). Again, if only one screed plate ispresent, only one of the heating elements may be heated at a time. Ifmultiple screed plates are present, those heating elements associatedwith one screed plate may be heated together. Still further, as with themain screed plate that is divided into two sections, those heatingelements associated with one section of the screed plate may beenergized first, followed by the energizing of the heating elements ofthe other section of the screed plate.

After the screed plates have reached their predetermined temperatures,the screed plate temperatures are monitored (S13). If a screed platetemperature falls below the predetermined temperature Ta (S14), e.g.,250° F., the temperature switch of that screed plate closes and thecontroller notifies the associated output to energize the correspondingheating elements (S15). While these heating elements are beingenergized, other temperature switches may close as other screed platetemperatures fall below 250° F. However, these screed plates are notheated until the heating of the previous screed plate is completed. Ifmore than one temperature switch closes at the same time, the controlleractivates the outputs for only one of the screed plates at a time, in arandom order.

According to the present invention, the controller can be programmedaccording to the operator's need or the requirements of a particularpaving operation. For example, the controller can be programmed toalternately heat each screed plate, or section of a screed plate.Further, the controller can be programmed to heat first one plate, thantwo plates, or any pre-selected combination of plates in order toprovide optimum heating conditions while conserving power.

INDUSTRIAL APPLICABILITY

In operation, the on/off switch 70 on the controller 62 selectivelyconnects the 24V power supply 60 to the controller 62. When the on/offswitch 70 is positioned in an ON position, an automatic mode of theheating control system 14 is initiated. In the automatic mode, thecontroller 62 is programmed to limit the number of plates or sectionsthat can be activated at a time. For example, only one of two outputswitches that control heaters in the first and second screed sections18,20 or left and right screed extensions 30,32 is on at a time.Moreover, the controller 62 can be programmed to allow only one of theoutput switches that controls right or left hand side heaters of boththe extension and main screed plates to be on at one time, i.e., onlyone extending screed plate or section of the main screed plate can beheated at a time. This control can be variably programmed to have one ormore, but fewer than all of the heaters to be on at a time, as would beunderstood by one skilled in the art.

The warm-up switch 74 may be activated if it is desirable to heat morethan screed extension plate 40,42 or first and second section plate36,38 of the main screed plate 16 simultaneously. Such simultaneousheating may be desirable during initial start up of the paving machine12. When the warm-up switch 74 is activated, the controller 62 turns onall the outputs switches 100,102,104,106,110,112,114,116 at the sametime if all the temperature switches 80,82,84,86 are closed. Once thescreed plates 36,38,40,42 have reached their predetermined temperatures,the temperature switches 80,82,84,86 open, and the controller 62 returnsto automatic mode.

Also, the warm-up switch 74 overrides the automatic mode. Thus, when theautomatic mode is not providing the type of surface finish desired, dueto inadequate heating, the warm up mode can be activated. After all thetemperature switches open once, the controller 62 may go back to theautomatic mode. Alternatively, the warm-up mode may be manuallycontrolled. For example, the warm-up switch 74 also can act as anoverride for the warm-up mode. Thus, if the operator determines that theappropriate surface finish is being achieved, the warm-up switch 74 canbe operated again, and the controller 62 will go back to automatic mode.

During normal operation the screed plates 36,38,40,42 will cool down andthe temperature switches 80,82,84,86 will close. The temperature sensors90,92,94,96 detect the temperature of the corresponding screed plate36,38,40,42 and when the temperature falls below a predetermined level,the temperature switch 80,82,84,86 closes. The controller 62 receives asignal that the temperature switch 80,82,84,86 has closed and that thecorresponding screed plate 36,38,40,42 should be heated. The controller62 will energize the resistive heating element or elements correspondingto that screed plate 36,38,40,42 in the time sequenced order in whichthe temperature switches close. For example, if temperature switch 80closes first, outputs 100, 110 turn on, and then when anothertemperature switch 84 closes, the controller 62 detects the closing butit waits for outputs 100,110 to turn off before issuing a signal to theappropriate relay to turn on the next outputs 104,114. If multipletemperature switches close while an output is on, then the next outputsassociated with a particular screed plate or section will be turned onin the order in which the temperature switch is closed.

With this automatic mode, only one screed plate 36,38,40,42 can beheated at a time, thus, conserving power for other operations of thepaving machine 12. For example, with conventional heating systemsseveral screed plates may be heated simultaneously. This depletes powerfrom other functions, for example, the paving machine speed may slowdown, thus slowing down paving operations and affecting road quality.With the present invention, only a limited amount of power is used toheat the screed plates at any given time, and thus other functions ofthe paving machines are not affected during normal operation.

In general, only certain screed plates require heating due to the mannerin which the asphalt material interacts with the screed plates. Forexample, during paving operations, high temperature asphalt material isconveyed from the paving machine 12 onto the roadbed surface. This hightemperature asphalt material reaches the center portions (i.e., mainscreed 16) of the screed assembly 10 first, since the material isconveyed from a central portion of the paving machine 12, and then tendsto spread toward the left and right screed extensions 18,20. Since theasphalt material temperature lowers from the time it contacts the mainscreed 16 to the time it contacts the left and right screed extensions18,20, the left and right screed plates 40,42 are influenced less by theasphalt temperature. Thus, the left and right screed plates 40,42 tendto require more heating than the first and second screed plates 36,38.

The both/rear only switch 72 distinguishes the forward outputs100,102,104,106 from the rearward outputs 110,112,114,116. When theboth/rear only switch 72 is off, i.e., “both” is activated, all outputs,forward 100,102,104,106 and rearward 110, 112,114,116, are enabled.However, when the both/rear-only switch 72 is on, i.e., “rear-only” isactivated, only the rear output switches 110, 112,114,116 can be closed.

For example, if the rear-only switch 72 is on, only the temperatureswitch 116 for the right screed plate 42 can close, and thus only therearward resistive heating elements 56 c,56 d associated with thetemperature switch 116 are energized accordingly.

This feature provides for a more efficient use of the power supply 60under certain conditions. Namely, those conditions are where only therearward portion of the screed plate needs to be heated, making itinefficient to energize the forward resistive heating elements. Thiscondition may be preferred due to the manner in which the heated asphaltmaterial interacts with the screed plates. For instance, when theasphalt material is first conveyed from the paving machine 12 onto theroadbed it has a high temperature. This high temperature asphaltcontacts the front portions of the screed plates 36,38,40,42, and thenreaches the back portions of the screed plates 36,38,40,42 as the screedassembly 10 travels over the asphalt material. However, the temperatureof the asphalt material lowers by the time it reaches the back portionsof the screed plates 36,38,40,42. Thus, the rear portions of the screedplates 36,38,40,42 are not as influenced by the heated temperatures ofthe asphalt material, as compared to the front portions of the screedplates 36,38,40,42. Thus, under certain conditions, it may be desirableto only energize the rearward resistive elements in order to conservepower of the paving machine.

During initial start-up of the paving machine 12, all of the temperatureswitches 80,82,84,86 will probably be closed since the screed platetemperatures will be low from lack of use. If the controller 62 is setto automatic mode, there is no priority of turning on the outputswitches 100, 102,104,106,110,112,114,116, and they can be randomlyactivated. Alternatively, the controller 62 can be programmed to heatthe screed plates 36,38,40,42 in a predetermined order.

Of course, automatic mode can be overridden by initiating the warm-upmode in which case all the outputs would be activated at the same timeas described earlier.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit or scope of the invention. Forinstance, additional outputs may be provided to more specificallycontrol each individual heating element, or more or less heatingelements may be provided to more specifically control the heating ofeach screed plate. Thus, it is intended that the present invention coverthe modifications and variations of the invention provided they comewithin the scope of the appended claims and their equivalents.

Other aspects, objects and advantages of this invention can be obtainedfrom a study of the drawings, the disclosure, and the appended claims.

1-15. (canceled)
 16. A method for heating a screed assembly of a pavingmachine, the screed assembly including a screed plate and a plurality ofresistive heating elements positioned adjacent to the screed plate,comprising the steps of: sequentially and automatically energizing fewerthan all of the plurality of resistive heating elements at a time toachieve a predetermined screed plate temperature.
 17. The method forheating a screed assembly according to claim 16 further including thesteps of: de-energizing the energized fewer than all of the plurality ofresistive heating elements; and energizing a next fewer than all of theplurality of resistive heating elements.
 18. The method for heating ascreed assembly according to claim 16 where one of the plurality ofresistive heating elements is energized at a time.
 19. The method forheating a screed assembly according to claim 16, further including thesteps of: energizing all of the plurality of resistive heating elementssimultaneously upon initial start-up of the paving machine to achievethe predetermined screed plate temperature; and monitoring thetemperature of the screed plate thereafter.
 20. The method for heating ascreed assembly according to claim 16, wherein the screed assemblyincludes a plurality of screed plates, each having a plurality ofresistive heating elements, further including the step of: automaticallyenergizing one of the plurality of resistive heating elements at a timein a time sequence that is a function of the time sequence in which eachof the screed plates reaches a second predetermined temperature.
 21. Themethod for heating a screed assembly according to claim 20, before theenergizing step including the steps of: energizing all of the pluralityof resistive heating elements of all of the screed plates simultaneouslyupon initial start-up of the paving machine to achieve the predeterminedtemperature for all of the screed plates; and monitoring thetemperatures of the screed plates thereafter.
 22. The method for heatinga screed assembly according to claim 16, wherein at least one of theplurality of resistive heating elements is disposed adjacent to aforward portion of the screed plate and at least one of the plurality ofresistive heating elements is disposed adjacent to a rearward portion ofthe screed plate including the step of: energizing only the plurality ofresistive heating elements disposed adjacent to the rearward portion ofthe screed plate.
 23. The method for heating a screed assembly accordingto claim 16, wherein the screed assembly includes a plurality of screedplates each having a plurality of resistive heating elements, at leastone of the plurality of resistive heating elements being disposedadjacent to a forward portion of the corresponding screed plate and atleast one of the plurality of resistive heating elements being disposedadjacent to a rearward portion of the corresponding screed plate furtherincluding the step of: energizing only the plurality of resistiveheating elements disposed adjacent to the rearward portions of thescreed plates. 24-29. (canceled)
 30. The method for heating a screedassembly according to claim 16, wherein the screed plate is selectedfrom among a plurality of screed plates included on a paving machinescreed.
 31. The method for heating a screed assembly according to claim30, wherein the plurality of resistive heating elements positionedadjacent to the screed plate include a first heating element operativelypositioned with respect to the screed plate and a second heating elementoperatively positioned with respect to the same screed plate as thefirst heating element, the first and second heating elements both beingconfigured to apply heat to the screed plate, further including the stepof: selectively energizing the first heating element and the secondheating element such that there is at least some period of time whenheat is applied to the screed plate from only one of the first heatingelement and the second heating element.